Analyzing Electrocorticography Data

Module information
Modules	BESA Research Basic or higher
Version	BESA Research 5.2 or higher

There is increasing interest in using ECoG data in a quantitative manner. BESA Research offers a variety of tools for the processing of intracranial channels, which can prove extremely useful when analysing these data. Intracranial channels are assigned to a specific channel group (either PGR – polygraphic, or ICR – intracranial). It is then possible to perform the following types of analysis (and more).

• Pattern search. This can be very useful in order to identify similar events that happen either in one or in several channels. Simply select one or several channel labels using the CTRL key and the mouse button, mark a block over a pattern of interest, and press the “SAW” button (or “SAV” button if your are using the BESA Research options for EEG review) to start the pattern search. At the end of the search, you will have all similar events marked by tags, which can be converted to triggers, too, if further event-related processing is to take place.

• Trigger generation. Another way of finding and tagging similar events is the Schmitt trigger dialog which is reached from “ERP | Create triggers from EMG/EEG”. You are best to mark an event of interest first. Then open the dialog, select the channel of interest from the dropdown, and play around with additional filter settings, viewing the results with the “View Current Settings” button until the channel signal rises over a threshold (you can manually adjust the threshold in the viewing window). Pressing the “Search Selected” button in the dialog will find all events with similar spiking and tag them with a trigger code for further analysis like averaging, or time-frequency analysis.

• FFT analysis. FFT analysis can be performed on all types of channel data, and ECoG is no exception. It can give you great insights into the frequencies at play in your intracranial recording. Simply mark a block over the interval of interest, and press the “F” button to invoke FFT. Note that frequency bands can be freely adjusted in the FFT result window.

FFT analysis of intracranial EEG data

• Time-frequency analysis. This feature requires a source coherence module. It is quite straight forward once you have created some triggers marking your events as mentioned above. You should create a montage that contains just the intracranial channels you are interested in (using the Montage Editor). Then, open the ERP paradigm editor to define trigger values to average over, epochs, and filters, and use the Coherence tab to perform the analysis.

Time-frequency analysis of intracranial EEG data